The Diagnostic and Statistical Manual, version 5 (DSM-5) will soon be officially released. This is the American Psychiatric Association’s official taxonomy of the mental disorders and the criteria that clinicians should use to identify and treat them. (And to bill insurance companies for them.) The DSM is designed to be a kind of periodic table of the elements for mental health research and practice. Thus the publication of a new edition is an important event and changes to several diagnoses have incited controversy. And now one of the most important voices in mental health research has weighed in on DSM-5.
Thomas Insel, a psychiatrist, is the director of the National Institute of Mental Health. Through its funding of university research and its intramural labs, the NIMH is the leading engine of mental health research in the world. So Insel’s views matter. As it happens, he keeps a blog. You might expect that a blog post from a high government official would be sanitized and boring, but Insel’s post on 2013-04-29 was breathtaking.
Insel regrets the lack of scientific ambition shown in the “tweaking” and “modest alterations” of the DSM-5. What he is really concerned about, however, is not the details of individual diagnoses, but the architecture of the taxonomy itself. The DSM presents a world of discrete diagnoses such as “Attention Deficit Hyperactivity Disorder” or “schizophrenia”. In the world as DSM sees it, you either have one of these disorders or you do not. Insel doesn’t buy it:
The weakness [of each of the editions of DSM] is its lack of validity. Unlike our definitions of ischemic heart disease, lymphoma, or AIDS, the DSM diagnoses are based on a consensus about clusters of clinical symptoms, not any objective laboratory measure. In the rest of medicine, this would be equivalent to creating diagnostic systems based on the nature of chest pain or the quality of fever. Indeed, symptom-based diagnosis, once common in other areas of medicine, has been largely replaced in the past half century as we have understood that symptoms alone rarely indicate the best choice of treatment.
These problems have been debated for decades and were recognized by the intellectual leaders of the DSM-5 project, including its chair (and my old boss), David Kupfer. Kupfer had hoped that the DSM would be able to shift to an ontology of mental illness characterized by continuous dimensions that describe the functioning of primary mental systems governing cognition, mood, and behaviour. Instead of falling into one or more diagnostic categories, each of us would be a point in a space of mental functioning defined by these dimensions. The dimensions would be grounded in biomarkers and quantitative assessments of cognition and mood. The NIMH has also been interested in developing a dimensional system, called the Research Domain Criteria (RDoC) project.
In my view, there are many scientific and clinical reasons to believe that mental health assessment should be dimensional. However, neither the DSM-5 nor the RDoC projects have come up with a dimensional system that is ready for clinical use. Insel writes of RDoC that
It became immediately clear that we cannot design a system based on biomarkers or cognitive performance because we lack the data.
Similarly, the plan to develop a dimensional system for DSM-5 was a moonshot: a high-risk, high-reward, and high-cost effort. Unfortunately, it blew up on the launch pad. Not only did the projects require more data than could be collected in available time, but we may also need revolutionary advances in the many fields of neuroscience and psychology on which psychiatry rests.
Neither Kupfer nor Insel are giving up on the ambition to create a dimensional system. But what is the status of the about-to-published DSM-5, which retains the categorical system? Insel writes:
In this sense, RDoC is a framework for collecting the data needed for a new nosology. But it is critical to realize that we cannot succeed if we use DSM categories as the “gold standard.” The diagnostic system has to be based on the emerging research data, not on the current symptom-based categories. [Emphasis added.]
The quote in bold is extraordinary. “Gold standard” is a term of art in medicine. A gold-standard measurement system is supposed to be the reference used to anchor discussion and DSM has for decades been treated as the gold standard in American mental health research. Insel has withdrawn the NIMH’s scientific imprimatur from the DSM.
The NIMH’s views will not have a large effect on clinical practice. Clinicians currently using the DSM are unlikely abandon it without an alternative. The obvious current alternative, the World Health Organization’s ICD-10, is also categorical.
Insel’s is being candid about a debacle for the American Psychiatric Association. But this isn’t a scandal. Rather, it is progress for mental health research. We need to place mental health assessment on new foundations, but that does not imply that mental health research has no foundations. Science is just hard: you can’t easily test a theory without well-developed instruments, but how do you build a good instrument when you don’t yet have a solid theory? With NIMH’s support, investigators will have new freedom to shape research questions that can lead to progress.